Method and system for controlling ventilation

ABSTRACT

Internal climate comfort in a living room occupied by human users is controlled by natural ventilation, through at least two external adjustable openings and at least one internal opening, said natural ventilation being determined from a constant physical parameter of said living room and measured parameters relating to wind load and temperature difference to approximate a target air exchange rate for the room. An adjustment parameter (S 1 , S 2 ) for each external opening is determined to provide air exchange (Q f ) to the room on the basis of said target air exchange rate and is modified by application of a set of individual comfort functions (μ) for each opening, taking account at least of outside and inside temperature, air exchange and wind speed and direction. The individual comfort functions (μ) of said set are weighed by fuzzy optimization to produce optimized and substantially equally distributed comfort conditions in positions in the living room adjacent each opening.

The present invention relates to a computer controlled method ofcontrolling internal climate comfort by natural ventilation in a livingroom in a building occupied by human users, said room being connectedwith the outside of the building through at least two external openingswith associated passive ventilation devices, which are individuallyadjustable by means of associated operator units and being furtherconnected through at least one internal opening with another room of thebuilding, whereby a target air exchange rate for said living room iscalculated from a constant physical parameter of the room and measuredparameters relating to wind load or air pressure and :to differencebetween indoor and outdoor temperatures.

Computer controlled methods and systems for heating, ventilation and airconditioning in buildings are well known and conventionally based on theuse of active heating, ventilation and air humidity control devices.Various designs of such systems are described e.g. in U.S. Pat. No.4,567,939, U.S. Pat. No. 4,931,948, U.S. Pat. No. 5,215,498, U.S. Pat.No. 5,348,078, U.S. Pat. No. 5,803:,804, DE-A-196 00 694 and EP-A-0 585133.

It is well-known that such an active indoor climate adjustment doesusually not function in the best possible way under variable outdoorclimate conditions and furthermore is attended by a considerable energyconsumption.

On this background, recent years have shown an increased interest forusing controlled natural ventilation for indoor climate adjustment. Bycontrolled natural ventilation is in this connection meant adjustment ofthe indoor climate in a building by use of natural variation in outdoorand indoor climate variables and by ventilation air supply throughadjustable openable parts or sections of building facades. Such openableventilation devices are typically window sections in the buildingfacades, however, they may also comprise other forms of openable facadeparts, such as adjustable ventilation dampers, grids and similardevices.

Experimental projects to illustrate the possibilities of natural indoorclimate adjustment by use of intelligent computer systems are describede.g. by J. I. Kindangen in his report “Artificial neural network andnaturally ventilated buildings” in Building Research and Information,Vol. 24, no. 4, 1996, and by D. Azzi, G. S. Virk, A. K. M. Azad and D.L. Loveday in a conference paper “Towards the “intelligent building”” atthe 18th AIVC Conference in Greece in 1997, whereas control strategiesherefor are described by A. J. Martin in “Control of NaturalVentilation”, BSRIA Technical Note TN 11/95. The purpose of theseexperiments has essentially been to describe different parameter modelsfor pure computer controlled adjustment of various forms of adjustableheating, ventilation, shading and humidity control devices.

U.S. Pat. No. 5,226,256 discloses a method of the above type, by whichpassive ventilation devices in the form of windows can by means ofsensors adapted for the purpose be adjusted in dependence of indoorclimate variables, such as temperature, relative air humidity and CO₂content and external parameters as for instance noise conditions in thesurroundings and the airflow velocity near a window. For this adjustmenteach window is associated with a microprocessor which can also becontrolled from a portable or stationary remote control unit just as allwindows can be controlled jointly from a central control unit in acontrol room.

On the basis of this prior art it is the object of the invention toprovide an optimized method for automatic computer controlledventilation of living rooms in buildings, by which inconveniences, suchas the feeling of draught under cold weather conditions, resulting fromthe supply of fresh air to a living room by the flow of air throughexternal openings such as opened windows can be significantly reducedand an increased and well distributed internal climate comfort can beobtained.

To fulfil this object the method according to the invention ischaracterized in that an adjustment parameter for the operator unit ofeach of said passive ventilation devices is determined to provide an airexchange to the room on the basis of said target air exchange rate, saidadjustment parameters being further modified by application of a set ofcomfort functions, which are established individually for each of saidexternal and internal openings, said comfort functions being determinedto take account at least of outside and inside temperature, air exchangeand wind load or air pressure and the comfort functions of said setbeing weighed by fuzzy optimization to produce optimized andsubstantially equally distributed comfort conditions in positions in theliving room adjacent each of said openings.

Whereas some principles of general application of fuzzy logic operationsto building climate control have been described in a publication by theFrauenhofer Institute for Information and Data Processing IITB TH.Bernard and H.-B. Kunze “Multi-objective Optimization of BuildingClimate Control Systems using Fuzzy-logic”, the invention is based onthe recognition of the fact that no universal model can be realisticallyapplied to describe human comfort perception, but that normalizedperformance criteria can de described as fuzzy membership functions,which can be optimized by the use of fuzzy optimization

Preferred ways of implementation of the method are stated in dependentclaims 2 to 6.

According to the invention the method is carried out by means of acomputer controlled system for natural ventilation in a living room in abuilding occupied by human users, said room being connected with theoutside of the building through at least two external openings withassociated passive ventilation devices, which are individuallyadjustable by means of associated operator units and being furtherconnected through at least one internal opening with another room of thebuilding, said natural ventilation being determined from a constantphysical parameter of said living room and measured parameters relatingto wind load or air pressure and difference between indoor and outdoortemperatures to approximate a target air exchange rate for said livingroom, said system being characterized by comprising a computer deviceand sensor means for sensing said wind load or air pressure and saidtemperature parameters and inputting corresponding wind and temperaturedata to said computer device, said computer device having means forstoring a target air exchange rate for said living room, means fordetermination of an adjustment parameter for the operator units of eachof said passive ventilation devices to provide an air exchange to theroom on the basis of said target air exchange rate, means forestablishing a set of comfort functions individually for each of saidexternal and internal openings to take account at least of outside andinside temperature, air exchange and wind load or air pressure, andmeans for modification of said adjustment factors by application of saidset of comfort functions weighed by fuzzy optimization to produceoptimized and substantially equally distributed comfort conditions inpositions in the living room adjacent each of said openings.

Preferred embodiments of the system according to the invention arestated in dependent claims 8 to 11.

In the following the invention will be further explained with referenceto the accompanying schematical drawings, in which

FIG. 1 is a schematical sectional view of a living room in a buildinghaving two external openings in the form of openable windows and beingconnected with another room in the building through an internal openingin the form of a door;

FIG. 2 is a graphic representation of the relationship betweenadjustment parameters for the two windows shown in FIG. 1 atpredetermined air exchange rates;

FIG. 3 is an idealized graphic representation of user comfort as afunction as a function of air exchange to a living room;

FIGS. 4, 5 and 6 are graphic representations of comfort functions for anopenable window, an internal opening and air exchange, each showingperceived comfort level as a function of relative air flow;

FIG. 7 is a flow diagram of a preferred implementation of the methodaccording to the invention; and

FIGS. 8 to 11 are graphic representations of sets of comfort functionsweighed by fuzzy optimization and illustrating variations in dependenceon difference between outside and inside temperature and air exchange.

FIG. 1 is a simplified vertical sectional view of a living room in abuilding having two external openings in the form of openable windows 1and 2 and an internal opening in the form of a door 3. Each of windows 1and 2 is shown as a top hung window having a sash structure which from afully closed position can be opened to any position within a range ofventilation positions by automatic control. As schematically illustratedwindows 1 and 2 are provided with operator units 4 and 5, e.g. in theform of chain operators having a drive unit, arranged e.g. at a bottommember of the main frame structure, comprising an electric motor andengaging an elongate chain 6 and 7, respectively, the free end of whichis connected with the bottom member of the sash structure in a mannernot illustrated in detail.

To each of operators 4 and 5 an adjustment parameter defining the sizeof the ventilation opening of window 1 and 2, respectively, may besupplied from a central control unit in the form of a computer 9. Sincein the illustrated example the size of the ventilation opening isunambiguously defined by the adjusted length of chains 6 and 7,respectively, the variable adjustment parameter for each window may bedefined as the length s of the chain, which is determined by the numberof increment steps of a chain wheel engaging the respective chain.

In the situation illustrated in FIG. 1 a wind load is acting in adirection shown by arrow 8 substantially at right angles to the buildingfacade in which the window 2 is arranged. With both of windows 1 and 2as well as door 3 in open positions air flows Q₁, Q₂ and Q₃ will bedirected through each of openings 1, 2 and 3, of which air flow Q₂ isdirected from the outside into the living room,; whereas air flows Q₁and Q₃ are directed outwards from the room.

For the conduct of the ventilation method of the invention air flows Q₁,Q₂ and Q₃ are further determined by the difference between the outsideair pressure P₁ and P₂ in front of each of external window openings 1and 2, respectively, and the inside pressure in the room P_(i). Theoutside pressure in front of each window is determined by the wind loadand a window constant dependent on the architecture and the location ofthe window with respect to the wind direction. Wind load and directionis measured by a wind sensor 10, where-as outside and insidetemperatures T_(o) and T_(i), respectively, are measured by temperaturesensors 12 and 13. From each of sensors 10, 12 and 13 input data aresupplied via lines 14, 15 and 16 to central control unit 9, which viaoutput lines 17 and 18 supplies output data to operator units 4 and 5,respectively, for variable opening of windows 1 and 2 within theirranges of ventilating positions by adjustment of the respective chainlengths s₁ and s₂ of chains 6 and 7, respectively. As an alternative towind sensor 10 measurement of outside and inside air pressure could beeffected directly by pressure sensing by means of suitable pressuresensors.

Since as mentioned above the air flows Q₁, Q₂ and Q₃ through openings 1,2 and 3 may have either of two opposite directions, i.e. from theoutside into the room and vice versa, the flow direction will beindicated in the calculations developed in the following by applicationto the numerical value of the corresponding volumetric flow rate of apositive sign for the direction outside-in and a negative sign for thedirection inside-out.

For a satisfactory ventilation and internal climate comfort in theliving room a target air exchange rate is determined and expressed asthe volumetric flow rate of the fresh air supply needed to effect apredetermined number of total air exchanges pr. time unit.

For the air flows Q₁, Q₂ and Q₃ the following basic continuity conditionwill apply to indicate that the amount of air flowing into the roomshould be equal to the amount discharged from the room

Q ₁ +Q ₂ +Q ₃=0  (1)

On an empirical basis the actual fresh air supply Q_(f) to the room willbe related to the numerical volumetric rates of air flows Q₁, Q₂ and Q₃through openings 1, 2 and 3 as follows

Q _(f)=(|Q ₁ |+|Q ₂ |+|Q ₃|)/2  (2)

It will easily be appreciated that the air supply Q_(f) can be obtainedduring the opening periods for windows 1 and 2 by a multiplicity ofdifferent combinations of the opening or flow areas of the two windows.For a top hung chain-operated window as illustrated in FIG. 1 theopening area A will be

A=s(2*h/2+w),  (3)

where s is the active length of the operator chain and h and w are theheight and width, respectively, of the air flow area.

Since the only variable parameter in this expression is the chain lengths the expression could be simplified into

A=C _(a) *s,  (4)

where C_(a) is a constant for the window opening area.

In FIG. 2 a graphic representation is shown illustrating how variousdefined target values of the actual air supply Q_(f) could beaccomplished by combination of various opening areas of windows 1 and 2in FIG. 1 defined by the respective chain lengths s₁ and s₂.

For each of windows 1 and 2 the flow rate Q_(n) will be determined by

Q _(n) =C _(dn) *C _(an) *s _(n)*(2(P _(n) −P _(i))/ρ)^(½,)  (5)

where C_(dn) is a window constant for window n dependent on the shape ofthe window and the design of main frame and sash profiles, whereas P_(n)is the outside pressure, e.g. caused by wind load, in front of thewindow and ρ is the air density, which is temperature dependent. As canbe seen this expression can be simplified into

Q _(n) =C _(wn) *s _(n)*(2(P _(n) −P _(i))/ρ)^(½,)  (6)

where C_(wn) is simply a window constant.

In the expressions (5) and (6) the outside pressure in front of a windowis determined by

P _(n)=0.5*C _(p) *ρ*v ²  (7)

where C_(p) is a window constant depending on the architecture of thebuilding and the location of the window with respect to the winddirection, whereas v is the wind speed.

By the method of the invention the ventilation and internal climatecomfort of a living room, e.g. as shown in FIG. 1, is controlled bycontrol of an adjustment parameter of a passive ventilation deviceassociated with each of the external openings of the room. In theexample in FIG. 1 the external openings are windows and the passiveventilation devices comprise the openable wings or sash structures ofsuch windows in combination with operator units, by which the sashstructure can be moved between a fully closed position and anyventilation position within a range of such positions. In theillustrated example, where the operator units are well known chainoperators the range of ventilation positions will be limited by amaximum open position corresponding to the maximum free length of thechain connecting the sash structure with the electric operator drivemechanism arranged on the main frame structure.

The aim of the method of the invention is to provide a ventilation withan optimized internal climate comfort by adjustment of the sameadjustment parameter for the operator unit of each of a number ofwindows in such a way that, while maintaining ventilation at a levelsufficient to approximate the target air exchange rate, substantiallyequally distributed comfort conditions are produced in positions in theliving room adjacent each of the openings, whereby account is taken alsoof an internal opening such as a door connecting the living room withanother room in the building.

As illustrated in the idealized graphical representation in FIG. 3 ofclimate comfort as a function of the actual supply of fresh air into aliving room the comfort perception applied in the method according tothe invention is based on the approach that between lower and higherranges of the air supply rate Q_(f), in which the comfort level μ isperceived as unpleasant due to insufficient air exchange, on one hand,and to draught and cold problems, on the other hand, there is an optimumair supply rate, at which the comfort level is perceived as optimum. Byapplication of this approach to positions in the room adjacent eachopening in the room corresponding optimized ventilation positions of thepassive ventilation devices associated with the external openings of theroom such as optimized open window positions can be determined.

In FIGS. 4 and 5 schematic graphic representations are shown of examplesof separate comfort functions for an openable window, such as windows 1and 2 in FIG. 1, and an internal opening such as door 3 in FIG. 1. Inboth figures the curves represent perceived level of comfort μ as afunction of the flow Q through the opening with the flow directionoutside-in represented by positive flow rate values and the flowdirection inside-out by negative values.

In FIG. 4 three curves are shown to illustrate the effect on theperceived comfort level of variations in the temperature difference ΔTbetween outside and inside temperature, curves A, B and C representingtemperature differences of 1°, 5° and 40°, respectively. Whereas for arelatively low temperature difference the comfort level μ decreases onlyrelatively slowly with increasing flow rate for the directionoutside-in, a significantly more rapid comfort reduction occurs at alarger temperature difference.

In the somewhat idealized representation in FIG. 4 it is assumed thatthe comfort level will be substantially unaffected by the flow rate forthe direction inside-out due to the fact that the temperature of theflow will substantially the same as the indoor temperature T_(i).

As seen in FIG. 5 the comfort level for an internal opening such as adoor can, for practical purposes, be assumed to be symmetrical in thesense that comfort reduction as a function of flow rate will normallynot vary from one flow direction to the other, provided the temperatureis substantially the same at both sides of the internal opening.

FIG. 6 illustrates the perceived level of comfort as a linear functionwith positive inclination of the actual net air supply Q_(f).

Whereas in the separate comfort functions illustrated in FIGS. 4 to 6the comfort level next to an external or internal opening is shown as afunction of the flow through that particular opening, it is essentialfor the method of the invention that the set of comfort functions asshown e.g. in FIGS. 4 to 6 are compared and weighed against each otherto provide a basis for adjustment of the adjustment parameter of each ofthe passive ventilation devices. The fuzzy optimization used in themethod according to the invention requires the comfort functions μ₁, μ₂and μ₃ for openings 1, 2 and 3 to be expressed as functions of a commonvariable and be entered into a common coordinate system.

According to the invention a convenient and preferred approach to thisproblem is to have all the comfort functions determined as functions ofthe adjustment parameters for the operator units of the passiveventilation devices, e.g. in the described embodiment the chain lengthss₁ and s₂ of the operator units of windows 1 and 2, respectively.

According to a preferred embodiment of the method according to theinvention a practical way to implement this approach involves, asillustrated in the flow diagram in FIG. 7, determination of the internalroom pressure P₁ expressed as a function of the chain lengths s₁ and s₂of the operator units of windows 1 and 2 at a given net air supply Q_(f)as provided by equations (1), (2), (6) and (7) above, followed bydetermination of the flow rates through openings 1, 2 and 3 as functionsof the chain lengths s₁ and s₂ at the given net air supply Q_(f).

Following the determination of flow rates through the external andinternal openings the combination of chain lengths s₁ and s₂ can besubstituted for the individual air flows Q₁, Q₂ etc. in the comfortlevel representations shown in FIGS. 4 to 6. As will be seen, with thisrepresentation the comfort curve will take the form of a spatial surfacein an orthogonal spatial coordinate system having s₁, s₂ and μ as axesand thereby all of the individual comfort functions μ₁, μ₂ etc. can berepresented as a landscape of intersecting spatial surfaces in the samespatial coordinate system.

For purposes of illustration, the comfort functions μ₁, μ₂ etc. for allopenings and the air supply Q_(f) are presented in the examplesillustrated by the graphic representations in FIGS. 8 to 11 as functionsof a single variable, i.e. the chain length s₁ Of window 1 in FIG. 1.

In the idealized examples in these figures the flow through the internalopening in the form of door 3 has further been disregarded.

Once the comfort functions μ are depicted as functions of the samevariable the fuzzy optimization implies that the minimum curve of theset of comfort curves is determined. For each set of values of theadjustment parameter the minimum is represented by the spatial curveproviding the lowest comfort level.

The optimized adjustment of the common variable for the set of comfortcurves, i.e. in FIGS. 8 to 11 the chain length s₁ is then determined bywell-known fuzzy optimization as the maximum value on the minimum curve.Once the optimized value of the chain length s₁ has been determined inthis way the value of the chain length s₂ needed to obtain a given netair supply Q_(f) can be determined from the relationship illustrated inFIG. 2.

In each of FIGS. 8 to 11 the curves μ₁ and μ₂ represent the flowdirections inside-out and outside-in as shown for windows 1 and 2 inFIG. 1, and the figures illustrates, like FIG. 4, the effect on theperceived comfort level of varying difference ΔT between outside andinside temperatures.

In case of a relatively moderate value of the temperature difference ΔTthe method of the invention can be practised in a continuous coolingmode, in which both of windows assume open position, while theadjustment of the chain lengths take account primarily of variations inwind load, i.e. wind speed and/or wind direction.

With larger temperature difference it is preferred however to practisethe method of the invention in an intermittent or pulse mode, by whichwindows 1 and 2 are intermittently opened and reclosed between the fullyclosed positions, and open positions as defined by the chain lengthsdetermined by the fuzzy optimization.

Within the scope of the invention other kinds of separate comfortfunctions may be established and take into account for control of theinternal climate comfort such as comfort functions relating specificallyto inside temperature, CO₂_content and humidity, optionally involvingthe use of separate CO₂ and humidity sensing means.

What is claimed is:
 1. A computer controlled method of controllinginternal climate comfort by natural ventilation in a living room in abuilding occupied by human users, said room being connected with theoutside of the building through at least two external openings (1,2)with associated passive ventilation devices, which are individuallyadjustable by means of associated operator units (4,5) and being furtherconnected through at least one internal opening (3) with another room ofthe building, said natural ventilation being determined from a constantphysical parameter of said living room and measured parameters relatingto wind load or air pressure and to difference (ΔT) between indoor andoutdoor temperatures (T_(I),T_(o)) to approximate a target air exchangerate for said living room, characterized in that an adjustment parameter(S₁,S₂) for the operator unit (4,5) of each of said passive ventilationdevices is determined to provide an air exchange (Q_(f)) to the room onthe basis of said target air exchange rate, said adjustment parametersbeing further modified by application of a set of comfort functions (μ),which are established individually for each of said external andinternal openings (1,2,3), said comfort functions (μ) being determinedto take account at least of outside and inside temperature(T_(I),T_(o)), air exchange (Q_(f)) and wind load or air pressure anddirection and the comfort functions of said set being weighed by fuzzyoptimization to produce optimized and substantially equally distributedcomfort conditions in positions in the living room adjacent each of saidopenings.
 2. A method as claimed, in claim 1, characterized in that allcomfort functions (μ) of said set are determined as functions of saidadjustment parameters (S₁,S₂) for the operator units (4,5) of saidpassive ventilation devices and are compared by said fuzzy optimizationto provide a minimum comfort function, that a target value of theadjustment parameters (S₁,S₂) for said passive ventilation devices isdetermined as a maximum value of said minimum comfort function, wherebya set of adjustment parameters (S₁,S₂) is determined to provide saidoptimized substantially equally distributed comfort conditions whilemaintaining the approximation to said target air exchange rate.
 3. Amethod as claimed in claim 2, characterized in that the flow througheach of said external and internal openings are determined by theexpressions Q ₁ +Q ₂ +Q ₃=0, Q _(f)=(|Q ₁ |+|Q ₂ |+|Q ₃|)/2, Q _(n) =C_(wn) *s _(n)*(2(P _(n) −P _(i))/ρ)^(½, and) P _(n)=0.5*C _(p) *ρ*v ²,where Q₁, Q₂ . . . Q_(n) are the air flows through each of said externaland internal openings, C_(wn) is a constant relating to a specificopening, P_(n) is the outside air pressure in front of a specificopening, P_(i) the internal air pressure in said room, ρ is air density,C_(p) is a window constant and v is the wind speed, followed bydetermination of said comfort functions μ as separate function of theflow (Q₁, Q₂ . . . ) through each of said external and internal openings(1,2,3), and determination of said internal pressure P₁, the flowthrough (Q₁, Q₂ . . . ) each opening and the perceived comfort level (μ)as functions of said adjustment parameters (S₁, S₂) and entering theresulting comfort function in a common coordinate system beforeconducting said fuzzy optimization.
 4. A method as claimed in claim 1,characterized in that said set of adjustment parameters (S₁, S₂) isdetermined in a continuous cooling mode to control said operator units(4, 5) to adjust said passive ventilation devices within a range ofventilation positions.
 5. A method as claimed in claim 1, characterizedin that said set of adjustment parameters (S₁, S₂) is determined in apulse mode for intermittent short term operation of said operator units(4, 5) to open and reclose said passive ventilation devices between aclosed position and any position within a range of ventilationpositions.
 6. A computer controlled system for carrying out a method asclaimed in claim 1, by natural ventilation in a living room in abuilding occupied by human users, said room being connected with theoutside of the building through at least two external openings (1, 2)with associated passive ventilation devices, which are individuallyadjustable by means of associated operator units (4, 5) and beingfurther connected through at least one internal opening (3) with anotherroom of the building, said natural ventilation being determined from aconstant physical parameter of said living room and measured parametersrelating to wind load or air pressure and difference (ΔT) between indoorand outdoor temperatures (T_(I), T_(O)) to approximate a target airexchange rate for said living room, characterized by comprising acomputer device (9) and sensor means (10, 12, 13) for sensing said windload or air pressure and said temperature parameters and inputtingcorresponding wind and temperature data to said computer device (9),said computer device (9) having means for storing a target air exchangerate for said living room, means for determination of an adjustmentparameter (S₁, S₂) for the operator units of each of said passiveventilation devices to provide an air exchange (Q_(f)) to the room onthe basis of said target air exchange rate, means for establishing a setof comfort functions (μ) individually for each of said external andinternal openings to take account at least of outside and insidetemperature (T_(I), T_(O)), air exchange and wind load or air pressure,and means for modification of said adjustment factors (S₁, S₂) byapplication of said set of comfort functions weighed by fuzzyoptimization to produce optimized and substantially equally distributedcomfort conditions in positions in the living room adjacent each of saidopenings.
 7. A system as claimed in claim 6, characterized by comprisingmeans for shifting the operation of said computer device between saidcooling mode and said pulse mode of operation.
 8. A system as claimed inclaim 6, characterized in that said means for establishing saidindividual comfort functions and said means for modification of saidadjustment factors comprises means for carrying out fuzzy logiccomputing operations.
 9. A system as claimed in claim 6, wherein saidexternal openings (1, 2) are windows having a sash structure, which isopenable with respect to a stationary main frame structure within arange of ventilation positions between closed and fully open positions,and said associated operator units comprises a window operator unit foreach of said windows, characterized in that each of said operator units(4, 5) comprises a chain operator with an operator housing connectedwith an element of one of said sash and main frame structures andcomprising a drive unit and an elongate chain (6, 7) operable by saiddrive unit and connected at a free end with an element of the other ofsaid sash and main frame structures to provide a chain length betweensaid elements, which is variable to adjust said sash structure between afully closed position and any position within a range of ventilationpositions, whereby said adjustment parameter (S₁, S₂) is constituted bysaid variable chain length.